Complex technical systems, such as heating, ventilation, and air conditioning (HVAC) systems, in large buildings are subject to aging processes, operating errors, and other influences that may lead to hardware or software defects. When defects exceed certain limits, the defects may be referred to as faults that cause failures. Failures in the HVAC system may result in degraded energy efficiency, loss of user satisfaction, reduction of the lifetime of the system, or complete system malfunctions.
Only some severe failures are displayed as alarms by the HVAC system, while many malfunctions are not automatically noticed by occupants or system operators. Fault detection and diagnosis (FDD) systems detect all possible failures and localize the faults. Localizing the faults may reduce the time to find and repair faulty components and thus reduce maintenance cost and system down times.
Because of the diversity of buildings and HVAC systems, FDD systems may be specialized (e.g., HVAC system-specific). For example, the relations between the faults and the failures may be derived offline through exhaustive examination of the possible failures caused by each fault from a fault list for a given HVAC system. Single or multiple faults may be inserted into an off-line fault simulation, where failure rules may be exercised, creating the relations between the faults and the failures.
Fault-failure relations, however, depend on external influences such as outdoor temperature, manual set-points and space occupancy. With the exhaustive approach, the HVAC system-specific and condition-specific FDD systems may result in high computation time and cost.